What happens if I install a virtual machine additions package (e.g. Virtual Machine Additions for Microsoft Virtual PC 2007, Integration Components on Windows Virtual PC, and Guest Additions on Oracle VM VirtualBox) on a host PC? Will there be any adverse effects, or will my system work fine?

In other words, what happens in the backend on the virtual machine when I enable integration features like mouse pointer integration, window resizing, and folder sharing?

Disclaimer: I know that it is possible that this question could be marked as a duplicate of this one, but that one is asking about Ubuntu and VirtualBox specifically. My question is more general, and it also asks about how integration is internally implemented.

2 Answers
2

In general, guest additions install device drivers which auto-detect virtual hardware of a specific type and thereby enable some sort of "direct" host to guest interface that bypasses the typical VM<->host barrier to deliver improved usability.

Most sane guest additions packages will fail to install on a host because it attempts to detect whether it's running in a VM before installing. So the answer is probably "you will get an error and won't be able to install them". But on the off chance that you actually succeed in installing guest additions on the host, in most situations that will not have any visible impact, because the drivers will be placed there, but they won't be activated, because they won't detect the VM "virtual hardware" (some PCI ID or some specific character device (depending on platform and the particular hardware in question) indicating virtual hardware as opposed to physical).

A big part of these VM additions consists of special drivers for virtualized hardware (i. e. Virtualbox Soundcard Device, Virtualbox USB-Hostadapter and so on, same for VMware and others) so they won't get used because on the host system these devices don't exist.

Same for Desktop integration and so on, because these components cannot be used on a host system so the functions are not loaded into the running system.

The answer from the other post you mentioned should also be right for other operating systems.

I'm wondering specifically about mouse pointer integration. With integration features enabled, the mouse moves much faster, and, on the bottom and right edges, parts of the guest cursor are visible on the outside. With it disabled, the cursor moves more slowly. My suspicion is that with integration enabled, the cursor is actually a part of the host OS, and it sends the commands to the guest. I've heard reports that installing integration software on a host PC causes my cursor to disappear. Is that right?
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deletemeOct 15 '13 at 22:07